DNA, RNA and protein synthesis

Genes

• Genes are carried on DNA. A gene is a section of DNA that causes the production of protein which is the production of the animal or plant part. (Living material is built up by proteins.)
• Each one codes for a specific protein by specifying the order in which amino acids must be joined together.

GENE EXPRESSION

• Gene expression is the process by which inheritable information from a gene is made into protein or RNA.
• Gene expression functions in the environment of the living organism. 
• If the environmental factors are not correct then the characteristic produced by the gene may not be expressed. 
• The way an organism physically looks is called its phenotype. 

DNA

• DNA (deoxyribose nucleic acid) molecules are large and complex. 
• They carry the genetic code that determines the characteristics of a living thing.
• Except for identical twins, each person’s DNA is unique. 
• This is why people can be identified using DNA fingerprinting. 
• DNA can be cut up and separated, forming a sort of “bar code” that is different from one person to the next.

• DNA IS FOUND IN CELLS IN A TWISTED FORM CALLED A DOUBLE HELIX
•  This smallest unit of DNA is called a nucleotide.
• Coding DNA is an area of chromosome that produces chromosomes. Non coding DNA is an area of the chromosome that does not produce proteins

Structure of DNA

• DNA is composed of 4 bases. These bases go together in pairs. The 4 bases are known by the first letter of their name: A = Adenine, T = Thymine, G = Guanine, C = Cytosine.
• A can only join with T. G can only join with C. Each base pair has a purine and a pyrimidine
  
• The A and G bases are PURINES. The T and C bases are PYRIMIDINES.
  
• The forces holding the bases together are hydrogen bonds.
• Each pair of bases are held on the side strands of the DNA. 
• These side strands are made up of a pentose sugar (a 5-carbon sugar) and a phosphate group. 
• The entire unit is then made of three molecules: a pentose sugar (a 5-carbon sugar), a phosphate group a and a nitrogenous base. The pentose sugar is called deoxyribose. The phosphate is represented as P.

THE GENETIC CODE

• The genetic is the ability of 3 bases (or codon) in sequence to code for 1 amino acid; these amino acids in sequence to produce protein.
• Amino acids are made up of a set of 3 nucleotides called triplets or codons. 
• There are 20 amino acids that are used to form a variety of proteins. 
• There are many combinations of amino acids that make up the proteins that are an organism’s body.

DNA Replication

• It takes place during interphase of mitosis. 

• 1. Nucleotides are made in huge quantity in the cytoplasm.
  
• 2. An enzyme unzips the two complementary strands of DNA.
  
• 3. New complementary nucleotides link to the exposed bases on the separated strands.
• 4. A new complementary strand is built along each ‘old’ strand.
  
• 5. Two DNAs, identical to the original and each other, are now present. 

DNA Profiling

• DNA profiling is the process of making patterns of bands from a persons DNA to compare with other DNA patterns.
• The process identifies the DNA contained in a tissue sample, which is unique to each organism.
• The DNA is cut using enzymes and the segments are separated according to the size, using an electric current, along a piece of gel.
• The fragments are made visible by staining. The fragments form a pattern that can be analysed. A permanent record can be made of the pattern.

Applications

• DNA profiles can be used to identify people from crime sites, for paternity case, identifying pathogens or tissue matching

Genetic Screening 

• Genetic Screening is used to find out if the parents of a child or the child itself (through removal of cells from the foetus) carry defective genes that could develop into health problems. 
• Although the parent may not have the disorder he/she could be a carrier for the condition. 
• With genetic screening, prospective parents can determine if there is a possibility that their future children could have the health problem.

RNA

• Uracil takes the place of Thymine in RNA. So, the bases in RNA are:
  
• A = Adenine
• U = Uracil
  
• G = Guanine
  
• C = Cytosine
  
• A = Adenine is complementary (combines with) U = Uracil
  
• G = Guanine is complementary with C = Cytosine
  
• Unlike DNA, RNA is single stranded. 
• The RNA produced is complementary to the DNA which produced it. 
• Also, RNA can move out into the cytoplasm while DNA remains in the nucleus.
• GC, AU 

Types Of RNA

mRNA (messenger RNA):

• Produced in the nucleus. Used at ribosome to make protein.
• Copy of genetic message. Used as template to make protein.

rRNA (ribosomal RNA):

• A component of the ribosome.
• Reads the message on mRNA. Used to attach tRNA to the mRNA.

tRNA (transfer RNA):

• It attaches mRNA at the ribosome.
• Places amino acids in the correct sequence to make a protein.

mRNA and tRNA

Each mRNA strand carries:

• A start codon (AUG below)
  
• A series of codons each of which will form a particular amino acid
  
• A stop codon (UAA below)

Each tRNA is composed of:

• A codon of DNA which formed an amino acid
  
•  The tRNA itself
  
• A special anti-codon- each anti-codon is complementary to the amino acid codon. As a result, the tRNA and the mRNA are attracted to each other.

Protein Synthesis

• Each group of 3 bases (codon) along the DNA molecule will code for 1 of the amino acids that make up a protein.
• The order of bases along the DNA strand will therefore determine the protein that is made.
• The DNA is transcribed into mRNA. This mRNA will the nucleus and travel to the ribosomes where it is translated into protein structure.

Transcription (Is the copying of a section of DNA, a gene, into mRNA)

• Transcriptions occurs in the nucleus.
• DNA unwinds.
• The RNA  nucleotides are joined together and form mRNA.
• The mRNA leaves the nucleus.

Protein Synthesis

Translation (Is the manufacture of protein based on the sequence of bases on the mRNA)

• The mRNA arrives at the ribosome, the mRNA binds to the ribosomes.
• Ribosome is composed of rRNA and tRNA. 
• (tRNA) anti codon attaches to (mRNA) codon. 
• tRNA carries the amino acids,
• The correct order of amino acids are assembled to produce the necessary proteins